Topology optimization is a process of distributing material within a defined design space such that a performance objective for the part design may be achieved while satisfying the design constraints. In structural topology optimization, the objective is to minimize the compliance of the part design while reducing the part weight by a pre-defined factor. Topology optimization often returns geometry which can be described as organic in shape. Manufacturing these optimized part designs using conventional manufacturing techniques such as casting, forging, and extrusion often proves challenging, because of the inherent constraints of these traditional manufacturing methods. Manufacturing filters have been developed previously which incorporate these constraints of conventional processes within topology optimization. Some of the previously developed filters include uniform cross section enforcement for extrusion, and single and double draw direction enforcement for casting and forging. However, these filters significantly constrain the design freedom that comes with topology optimization and push the output to a sub-optimal design that is primarily restrained by the limited nature of the conventional manufacturing processes.
The timeline for the foundation and growth of topology optimization can be closely associated with that of additive manufacturing. Their combined potential to revolutionize the design and manufacturing industry by providing ultimate creative freedom, has made these technologies popular among engineering industries in recent years.
With the advent and subsequent improvements in additive manufacturing technology, the scope of part geometries which can be viably produced has increased dramatically. This state of the art manufacturing technology can be deemed as a close match for topology optimization (TO) because of its ability to manufacture complex shapes, obtained from TO, with significant ease. However, even additive manufacturing inherits certain issues which decrease the process efficiency in terms of time, cost and material usage, and which may result in failure during the part build process.
Additionally, additive manufacturing (AM) processes have seen a rapid growth of usage in the industry over the last decade. The freedom to manufacture complicated designs with ease, together with the absence of special tooling requirements have made it one of the most preferred manufacturing processes in a wide array of industries, such as toys, electronics, medical equipment, aerospace etc. AM encompasses many similar manufacturing processes which manufacture parts by layer-wise deposition of material. The first step of the process is slicing of the CAD model of the part at user defined intervals called slice thickness, along the build axis (usually z-axis) to generate 2D contours of the part at each level. This may be followed by the layer-wise deposition of material to create the 2D contours of the part at each level (Kulkarni and Dutta, 2000).
The methodology of material deposition may be dependent on the AM process being used. AM processes such as Selective Laser Melting (SLM), Direct Metal Laser Sintering (DMLS) and Selective Laser Sintering (SLS) use a high power laser beam to sinter/melt powdered material in each layer of a powder bed; while the Rapid Prototyping (RP)/Fused Deposition Modeling (FDM) process uses filaments of material passed through a heated die to deposit the molten material in sequential layers on the build platform (Kulkarni and Dutta, 2000). The sintered/deposited material adheres to the layer fabricated just before it. And thus, this cycle of melting and solidification may be repeated several times during the manufacturing process depending on the number of 2D slices generated from the CAD model. The heating and cooling of the material in the same layer may be uneven, and may be governed in principal by the laser scan/material deposition pattern (Das et al., 1998; Zhang et al., 2000; Chen and Zhang, 2007; Ning et al., 2005). The cumulative effect of these temperature differences over all the slices of material in the manufactured parts results in an isotropic shrinkage and deformation of the part, which has a significant impact on the part dimensional accuracy, and could also impede the functionality of the part.